A New Jersey power company said Friday it has reached an agreement to buy Salem Harbor Power Station and plans to build a state-of-the-art natural gas-fired plant on a piece of the 63-acre site while potentially opening the Salem waterfront to redevelopment.

Footprint Power LLC, of Bridgewater, N.J., said it would buy the aging plant and property for an undisclosed amount from Dominion Energy Inc., the Virginia company that has owned Salem Harbor since 2005. The companies gave no timetable for closing the deal, but a Footprint spokeswoman said the firm filed for expedited approval with the Federal Energy Regulatory Commission on Friday, and hoped to have a decision by the end of July.

If approved, the new natural gas plant would replace the current coal- and oil-fired facility, which is scheduled to be shut down in June 2014. City officials said more than half the waterfront property could then be open for redevelopment — with several possibilities, including opening a cruise ship terminal in Salem.

“They have a commercial pier that would be perfect for that,” said Mayor Kimberley Driscoll.

The agreement between Footprint and Dominion follows months of speculation about the future of Salem Harbor, which has operated in the city for six decades and is the city’s largest taxpayer. The plant employs more than 100 people.

In the last few years, Salem Harbor’s age, and tightening clean air regulations, made running the power station less and less economical, according to Dominion. On Friday, Jim Norvelle, a Dominion spokesman, said the company was pleased to find a buyer willing to keep the plant operating in some form. “We believe the transaction is a positive outcome for the plant employees, city of Salem, Footprint, and Dominion,” said Norvelle.

Salem Harbor would be the first acquisition for Footprint, a company formed in 2009 by power industry executives. Footprint has already requested a permit from ISO New England, the region’s grid operator, to start providing electricity by 2016.

While the proposed gas-fired plant is unlikely to employ as many workers as the existing facility, Footprint has indicated that Salem Harbor’s employees will be needed to help decommission the old plant and train workers for the new plant, said Richard Robey, spokesman for the International Brotherhood of Electrical Workers Local 326, which represents many of Salem Harbor’s employees.

“I think everybody is enthusiastic,” said Robey. “With Footprint, you know there are plans for [the plant] going forward — maybe the possibility for some commercial development.”

Though a new natural gas plant would be cleaner-burning, environmental advocates at the nonprofit Conservation Law Foundation in Boston, said it remains to be seen whether Footprint’s plans will — as claimed — help support increased use of renewable energy sources such as wind turbines and solar panels.

“We will scrutinize this proposal carefully to see whether it is truly capable of advancing a cleaner energy future,” said Shanna Cleveland, a staff attorney with the foundation.

Erin Ailworth can be reached at eailworth@globe.com. Follow her on Twitter @ailworth.